The invention relates to a luminaire, in particular a wall or ceiling luminaire protected against sprayed or splashed water, for receiving at least one elongated gas-discharge lamp, having an enclosure able to be assembled into a closed form from a transparent lower part which can be mounted in a fixed position and which holds electrical gear and a transparent upper part. Luminaires having gas-discharge lamps are generally particularly economical light-sources which can be operated with long lives and with a high light yield in relation to the electrical power which has to be applied. Widespread use is made of such lamps particularly in industrial areas and in domestic side rooms, where certain deficiencies in the spectral distribution of the light and particularly in the length and shape of the lamps impose restrictions in respect of the decorative design of luminaires but are not such an important consideration as in, say, the living area. Luminaires in industrial areas and in basements or garages are also very often subject to requirements for being of a construction which is at least protected against water and are, at the same time, usually highly developed mass-produced products whose price is keenly costed.
Known luminaires of this kind have a lamp enclosure which comprises a highly-transparent upper part and a non-transparent lower part. With a division of this kind, the non-transparent lower part may then be formed by a shell of synthetic resin which absorbs the heat which is given off by the lamps, particularly in the region of the electrodes at the ends, and above all the heat from a ballast (choke) which is arranged inside the lamp, whereas the upper part is produced from a highly transparent thermoplastic plastics material which makes possible the desired division of the radiated light but which has a very much lower resistance to temperature and a very much greater thermal expansion than the thermoset material of the lower part.
The terms “upper part” and “lower part” which are used here and which are commonly employed in German practice do not refer to the respective installed positions, and instead lower part denotes the body of the enclosure, which is to be fastened to a wall or ceiling and which generally also serves as a mounting for the electrical gear, whereas “upper part” denotes a cover which is detachably held by the lower part. It is thus possible, in the case of ceiling mounting say, for the upper part to be at the very bottom.
However, the lower part of non-translucent thermoset material, which is conventionally more resistant to thermal and mechanical stresses, absorbs a considerable proportion of the light which is emitted from the lamp or lamps inside the enclosure. What is more, the distribution of the light is unsatisfactory if large areas of shadow occur on the side on which the lower part is situated. Where mounting is on a wall or ceiling, dark shadowed zones giving an unwanted pattern of illumination then arise, particularly in the areas adjoining the luminaire.
What is more, attempts have already been made to produce trough-like luminaires of this kind which have a transparent lower part made of a material which is the same as or similar to the material of the upper part. However, it has been found that variations in the properties of the material result in mounting and sealing problems which cannot be solved, or at all events not at a cost that meets the demands of the market.
It is therefore an object of the invention to provide a luminaire of the kind considered here which makes possible improved light emission and light distribution without at the same time abandoning the standards of reliability and ruggedness, of easy mounting and handling and in particular of low-cost manufacture to which these lamps have been further developed.